This invention relates to golf balls and, more particularly, to wound golf balls with high specific gravity centers.
Conventional golf balls have been designed to provide particular playing characteristics. These characteristics are generally initial velocity, compression, and spin of the golf ball, and they can be optimized for various types of players. For instance, certain players prefer a ball that has a high spin rate in order to control the ball flight and stop the golf ball on impact with the greens. This type of ball, however, may not provide maximum distance. Other players prefer a ball that has a low spin rate and high resiliency to maximize distance.
Generally, golf balls have been classified as wound balls or solid balls. Wound balls are generally constructed from a liquid or solid center surrounded by an elastic thread wound in tension to form a wound core. This wound core is then surrounded by a cover. Wound balls are generally thought of as performance golf balls. When struck by a golf club, these balls have good resiliency, relatively high spin rate, and xe2x80x9csoftxe2x80x9d feel. Wound balls are generally more difficult to manufacture than solid golf balls.
Some early solid or non-wound golf balls contained metal. U.S. Pat. No. 4,995,613 to Walker discloses a practice golf ball with a dense metal-containing core surrounded with a thick layer of resilient material. To this, a fabric cover is bound. U.S. Pat. No. 5,104,126 to Gentiluomo discloses a non-wound ball that includes a dense center of steel surrounded by a molded encapsulating mass of a low density resilient synthetic elastomer composition. Both of these patents disclose solid or non-wound balls that include metal.
On the other hand, U.S. Pat. No. 1,946,378 to Young and U.S. Pat. No. 2,914,328 to Harkins disclose golf balls that include wound layers. For example, the Young patent discloses a spherical center weight of metal with an intermediate sphere of soft rubber thereon. Windings of rubber are disposed about the intermediate layer and an outer casing is formed thereon. Since high cis, polybutadiene was first introduced in 1956, the Young patent that was filed in 1931 and issued in 1934, did not disclose the use of such a compound. The commercial product related to the Harkins patent was the First Flight(trademark) golf ball. The Harkins patent does not disclose the use of polybutadiene and the First Flight(trademark) balls were not manufactured using polybutadiene.
The balls in Table I are formed with a steel inner sphere surrounded by an outer sphere or shell to form a center. The outer sphere is formed of natural rubber, designated NR, and possibly styrene butadiene rubber, designated SBR. No polybutadiene is used.
In conventional balls, when polybutadiene forms a core layer of the golf ball it typically includes enough high density fillers to alter the weight of such a layer. The amount of high density fillers used is, however, less than about 10 parts per hundred based upon 100 parts per hundred of polybutadiene. These fillers have two unfortunate side effects, they increase the hardness of the center and reduce the ball""s resiliency.
Therefore, a need exists for a golf ball with lower hardness or compression but with greater resiliency. The improved golf balls of the present invention to provide as disclosed herein provides such a golf ball.
The present invention is directed towards an improved golf ball that includes a high-specific gravity central sphere encapsulated in a soft and resilient shell layer.
In one embodiment, the sphere is formed of metal and the soft-resilient shell is formed of polybutadiene rubber molded thereon. This shell is subsequently wound with thread that is preferably elastic to form a wound core. This wound core is then covered. One feature of the metal sphere is that it has a specific gravity of at least about 6.0.
In this embodiment, the sphere has a sphere diameter less than about 0.5 inches and the subassembly with the shell has a shell diameter equal to or greater than about 1.3 inches. Further in this embodiment, the wound core can include a wound core diameter of greater than about 1.55 inches.
Preferably, the inventive golf ball has a compression of less than about 90, and more preferably the compression is between about 40 and about 80.
Preferably, the wound layer is formed of at least one spun elastic thread, and the sphere is formed of a solid metallic material. In this embodiment, the metallic material is formed from one of the following: tungsten, steel, brass, titanium, lead, zinc, copper, iron, silver, platinum, gold, or alloys thereof.
In another embodiment, the sphere is molded of high-specific gravity powder retained in a binding material. Preferably, the binding material is a thermoplastic compound, and the high specific gravity filler is metallic powder. A soft-resilient layer is disposed on the sphere and preferably is formed of polybutadiene rubber molded thereon. This layer is subsequently wound with thread that is preferably elastic to form a wound core. This wound core is then covered.
In yet another embodiment, the binding material can be a thermosetting compound.
According to one feature of this embodiment, the metallic powder is formed from one of the following: steel, brass, titanium, lead, zinc, copper, tungsten, bismuth, nickel, molybdenum, iron, bronze, cobalt, silver, platinum, gold, or alloys thereof. In addition, the sphere has a mass, the metallic powder forms a first percentage of the mass, the binding material forms a second percentage of the mass, and the first percentage is greater than the second percentage.
According to another embodiment, the wound golf ball of the present invention comprises a sphere having a specific gravity of above about 6.0, at least one molded shell, a wound layer, and a cover. The molded shell is formed around the sphere to form a center. The center has a diameter equal to or greater than about 1.25 inches. The wound layer is disposed about the center to form a wound core, and the cover surrounds the wound core.
In alternative embodiments, the center has a diameter of greater than about 1.3 inches or greater than about 1.4 inches.
In this embodiment, the sphere can be formed of a solid metallic material or of metallic powder retained in a binding material.
In yet another embodiment, the center further includes a first shell disposed on the sphere and a second shell disposed on the first shell, wherein the first shell is a molded layer and the second shell is a wound layer. According to one feature of this embodiment, the first shell has a first Shore D hardness and the second shell has a second Shore D hardness different from the first Shore D hardness by at least 5. The first Shore D hardness can be greater than or less than the second Shore D hardness.
The present invention is further directed to a wound golf ball that comprises a solid sphere formed of a metal material, at least one molded shell, at least one wound layer, and a cover. The molded shell is formed around the sphere to form a center. The shell includes a rubber material and has the center has a diameter greater than about 1.25 inches. The wound layer is disposed about the center to form a wound core, and the cover surrounds the wound core.
In one embodiment, the wound layer can be formed of a thread that includes a mixture of synthetic cis-1,4 polyisoprene rubbers, natural rubber and a curing system. Alternatively, the wound layer can be formed of a thread that includes a polyurea material. In another embodiment, the cover is formed of one of the following: balata, gutta percha, an ionomer or a blend of ionomers, polyurethane, polyurea-based composition, epoxy-urethane-based compositions, single sitexe2x80x94including metallocenexe2x80x94catalyzed polyolefins, cast elastomers, or combinations thereof.
In another embodiment, the sphere can have a diameter greater than about 0.4 inches, and/or an outer hardness of the wound core is greater than about 55 Shore D.
According to features of the present invention the golf ball cover includes at least two layers. In addition or in the alternative, this golf ball includes at least two wound layers.